Surface morphology, stress, and volume change during growth and crystallization of interface-stabilized amorphousFe100−xZrxfilms

Abstract

Thin ${\mathrm{Fe}}_{100\ensuremath{-}x}{\mathrm{Zr}}_{x}$ films, evaporated for $x<~7$ on top of a Zr substrate, show a glass-to-crystal transition in dependence of the film thickness. For $x>7$ the transition does not occur, and the film grows amorphous for any film thickness. With the help of in situ ultrahigh-vacuum scanning-tunneling microscopy and intrinsic stress measurements during film deposition, it is possible to investigate the described phase transition quantitatively, and to estimate the volume change of the film at the critical film thickness during crystallization. This allows an interpretation of the phase transition in terms of instability criteria for the crystal-to-glass transition. Using pure Fe on Zr provides the exciting opportunity of investigating surface topographs of monoatomic amorphous thin films, commonly not accessible for experiments. Just by tuning the film composition, totally amorphous film growth can be easily compared to crystal films, keeping primarily the material system unchanged. Thus, crystal-film growth can be characterized by columnar grain growth under strong tensile stresses, and amorphous films develop accordingly mesoscopic hill-like structures.